title: Collapse of long-range charge order tracked by time-resolved photoemission at high momenta.
abstract: Intense femtosecond (10(-15) s) light pulses can be used to transform electronic, magnetic and structural order in condensed-matter systems on timescales of electronic and atomic motion. This technique is particularly useful in the study and in the control of materials whose physical properties are governed by the interactions between multiple degrees of freedom. Time- and angle-resolved photoemission spectroscopy is in this context a direct and comprehensive, energy- and momentum-selective probe of the ultrafast processes that couple to the electronic degrees of freedom. Previously, the capability of such studies to access electron momentum space away from zero momentum was, however, restricted owing to limitations of the available probing photon energy. Here, using femtosecond extreme-ultraviolet pulses delivered by a high-harmonic-generation source, we use time- and angle-resolved photoemission spectroscopy to measure the photoinduced vaporization of a charge-ordered state in the potential excitonic insulator 1T-TiSe(2 )(refs 12, 13). By way of stroboscopic imaging of electronic band dispersions at large momentum, in the vicinity of the edge of the first Brillouin zone, we reveal that the collapse of atomic-scale periodic long-range order happens on a timescale as short as 20 femtoseconds. The surprisingly fast response of the system is assigned to screening by the transient generation of free charge carriers. Similar screening scenarios are likely to be relevant in other photoinduced solid-state transitions and may generally determine the response times. Moreover, as electron states with large momenta govern fundamental electronic properties in condensed matter systems, we anticipate that the experimental advance represented by the present study will be useful to study the ultrafast dynamics and microscopic mechanisms of electronic phenomena in a wide range of materials.
authors.affiliation: Institute of Experimental and Applied Physics, University of Kiel, 24118 Kiel, Germany.
authors.forename: Timm
authors.initials: T
authors.lastname: Rohwer
authors.forename: Stefan
authors.initials: S
authors.lastname: Hellmann
authors.forename: Martin
authors.initials: M
authors.lastname: Wiesenmayer
authors.forename: Christian
authors.initials: C
authors.lastname: Sohrt
authors.forename: Ankatrin
authors.initials: A
authors.lastname: Stange
authors.forename: Bartosz
authors.initials: B
authors.lastname: Slomski
authors.forename: Adra
authors.initials: A
authors.lastname: Carr
authors.forename: Yanwei
authors.initials: Y
authors.lastname: Liu
authors.forename: Luis Miaja
authors.initials: LM
authors.lastname: Avila
authors.forename: Matthias
authors.initials: M
authors.lastname: Kalläne
authors.forename: Stefan
authors.initials: S
authors.lastname: Mathias
authors.forename: Lutz
authors.initials: L
authors.lastname: Kipp
authors.forename: Kai
authors.initials: K
authors.lastname: Rossnagel
authors.forename: Michael
authors.initials: M
authors.lastname: Bauer